Hi,
I know "the internal render error: 5" can be caused by differing sizes or the EXIF information about the orientation of images. I am sure that my images are not of the same size because my macro lens has the external focusing mechanism and moves back and forth to focus on the object. I am not sure what macro lenses you are using. But most macro lenses have the external or extending focusing mechanism. That means that every image captured by this external focusing mechanism will be different in sizes and perspectives of objects in images. What can I do in this case a macro lens captures all images in different sizes? How do you make all images have the same size and perspective either by photography or by post-production?

You might want to make some changes to the Scale setting on the Edit/Preferences/AutoAdjustments page. But I've done 100+ image stacks with the camera on a tripod without seeing this error. And yes, there is a slight but noticeable focal length shift, but Helicon does not complain. If you are hand holding the camera, changes between shots may be too great.

Thanks, BoStone,
Now I realize that the size was not that of an object in images but the dimension of images (Width * Height).
I did the HDR merge with cropping and that changed the dimension of the images; that was the problem!
Now everything's fine.
Thank you!